This application proposes further follow-up of a birth cohort of children, initially established in the 1980s. The proposed funding period takes the children through their 16th birthday, when a comprehensive respiratory and allergy assessment will be conducted. This extended follow-up takes the cohort from birth to an age at which lung growth will be virtually complete for girls and ending its most rapid phase for boys. The resulting data set will be used to test diverse hypotheses concerned with lower respiratory tract illnesses (LRI), asthma, wheezing, allergy, and smoking. The application groups these into four broad areas: 1) effects of LRI during the first three years of life and early and late symptoms and allergic sensitization on the picture of asthma; 2) changes during adolescence in symptoms and airways responsiveness; 3) the natural history of allergic sensitization and its relation to asthma and asthma-like symptoms; and 4) the change in longitudinal lung function and factors affecting the change. A well documented data set is available to test these hypotheses. LRI were documented during the first three years of life, atopy has been evaluated, symptom status tracked, and lung function periodically measured. Infant lung function was assessed for a sample of the children and methacholine challenge was performed at age 11. In the evaluation at age 16 years, symptoms, lung function, including methacholine responsiveness, and atopy and lymphocyte phenotype will be assessed. Various methods for longitudinal data analysis will be employed.